CN109286585B

CN109286585B - Capture algorithm based on USB measurement and control system

Info

Publication number: CN109286585B
Application number: CN201810946886.7A
Authority: CN
Inventors: 杜检来; 方堃; 贺辉
Original assignee: SHANGHAI SCIENTIFIC INSTRUMENT FACTORY; Shanghai Aerospace Electronics Co ltd
Current assignee: SHANGHAI SCIENTIFIC INSTRUMENT FACTORY; Shanghai Aerospace Electronics Co ltd
Priority date: 2018-08-20
Filing date: 2018-08-20
Publication date: 2021-06-01
Anticipated expiration: 2038-08-20
Also published as: CN109286585A

Abstract

A capture algorithm based on a USB measurement and control system is characterized by comprising the following steps: step 1) initial capture stage: sending the filtered signal to an FFT spectrum analysis module, carrying out FFT operation on the input signal, comparing the processed signal with a judgment threshold after FFT judgment window processing, and selecting a frequency point higher than the threshold; step 2) judging whether the signal is valid: when the frequency points are symmetrical in amplitude and frequency distribution, the identified frequency is sent to a frequency mixing module for compensation, and a frequency locking ring is started at the same time; if the distribution of the frequency points does not show symmetry, judging that the input signal has interference or other abnormal conditions, and not passing the signal capture; step 3) in the tracking stage: the FFT spectrum analysis module keeps working, monitors the symmetry of the frequency spectrum, and if the frequency spectrum is abnormal, an error signal is given to the frequency locking ring for resetting.

Description

Capture algorithm based on USB measurement and control system

Technical Field

The invention relates to a capture algorithm based on a USB measurement and control system, which is applied to the fields of satellite measurement and control communication, satellite navigation, mobile communication and the like.

Background

With the deep development of aerospace technologies such as deep space exploration, manned aerospace, commercial aerospace and the like, the satellite measurement and control functions are more and more complex, and aerospace measurement and control systems with various different systems and functions are formed, but a unified S frequency band (USB) measurement and control system is still one of important measurement and control means. With the rapid development of digital signal processing technology, the USB measurement and control transponder is gradually realized by adopting an intermediate frequency digital processing mode so as to meet the requirements of universality, inheritance and flexibility of the aerospace measurement and control system.

In the digital processing of the USB measurement and control system, the capture of the residual carrier is beneficial to the synchronization and tracking of the subcarrier signal and the side tone signal. When the double capturing stage contains subcarrier signals or the input signals in the tracking stage are weak, so that the loop is temporarily unlocked and recaptured, due to the existence of large spectral lines on two sides of a residual carrier, the risk that the loop is locked to the wrong frequency in a wrong mode may exist.

Disclosure of Invention

Aiming at the risk that the loop is locked to the wrong frequency in a wrong mode, a capture algorithm based on a USB measurement and control system is provided, a capture tracking method combining FFT and a frequency-locked phase-locked loop is adopted, the characteristic of the symmetry of a PM signal frequency spectrum is utilized, the residual error frequency is captured rapidly, interference signals are judged according to the residual error frequency, the false locking of the receiving loop is effectively prevented, and the requirements of large dynamic Doppler change and low sensitivity of a USB measurement and control transponder are met.

The invention relates to a capture algorithm based on a USB measurement and control system, which comprises the following steps:

step 1): initial phase of capture

Sending the filtered signal to an FFT spectrum analysis module, carrying out FFT operation on the input signal, comparing the processed signal with a judgment threshold after FFT judgment window processing, and selecting a frequency point higher than the threshold;

step 2): stage for judging whether signal is effective

When the frequency points are symmetrical in amplitude and frequency distribution, the identified frequency is sent to a frequency mixing module for compensation, and a frequency locking ring is started at the same time;

if the distribution of the frequency points does not show symmetry, judging that the input signal has interference or other abnormal conditions, and not passing the signal capture;

step 3): in the tracking phase

The FFT spectrum analysis module keeps working, monitors the symmetry of the frequency spectrum, and if the frequency spectrum is abnormal, an error signal is given to the frequency locking ring for resetting.

Further, the capture algorithm based on the USB measurement and control system is characterized by comprising the following points:

1. in the initial capturing stage, an FFT spectrum analysis module performs FFT operation on an input signal in the Doppler range of the whole signal, compares the processed signal with a judgment threshold after FFT judgment window processing, and selects a frequency point higher than the threshold;

2. when the frequency points are symmetrical in amplitude and frequency distribution, judging that the input signal is effective, compensating the center value of the frequency points after the frequency points are sequenced in sequence to a frequency mixing module as a residual carrier frequency value, and simultaneously generating a starting signal for starting an FLL ring to work, wherein the FLL ring accurately tracks the residual carrier frequency; if the distribution of the frequency points does not show symmetry, judging that the input signal has interference or other abnormal conditions, and not passing the signal capture;

3. in the tracking stage, the FFT spectrum analysis module keeps working, the symmetry of the spectrum is monitored, if the signal spectrum is not symmetrical by taking the residual carrier as the center, the false lock state is judged, the signal acquisition and tracking are abnormal, the FFT spectrum analysis module generates an error indication signal to reset the FLL loop, and the local carrier frequency of the frequency mixing module is set as the center signal frequency detected by the FFT.

Compared with the prior art, the invention has the advantages that: the capture algorithm based on the USB measurement and control system is applied to the fields of satellite measurement and control communication, satellite navigation, mobile communication and the like, has high universality and wide range of applicable input amplitude, and is particularly suitable for measurement and control answering machines under the conditions of large dynamic Doppler change and high sensitivity. The intermediate frequency signal capturing and tracking algorithm of the USB measurement and control transponder, which combines the fast FFT capturing algorithm and the frequency locking phase-locked loop, is adopted, the characteristics of PM signal frequency spectrum symmetry, wide FFT spectrum analysis visual frequency range and high operation speed are fully utilized, the requirements of large dynamic Doppler change and high sensitivity are met, the wrong locking of a loop on a wrong frequency is effectively prevented, and the robustness and the reliability of the system are enhanced.

Drawings

Fig. 1 is a block diagram of an implementation of the capture algorithm based on the USB measurement and control system of the present invention.

Detailed Description

The invention is further illustrated by the accompanying drawings and examples.

Fig. 1 is a block diagram of an implementation of the capture algorithm based on the USB measurement and control system according to the present invention, which includes: mixing 0, low-pass filtering 1, FFT spectrum analysis 2 and frequency locking loop 3.

As shown in fig. 1, the input digital intermediate frequency signal and the SIN/COS signal generated by NCO are mixed separately to form orthogonal I-path signal and Q-path signal, and low-pass filtering is performed to filter out high frequency components.

And sending the filtered signal to an FFT spectrum analysis module, carrying out FFT operation on the input signal in the Doppler range of the whole signal so as to judge whether the signal is effective, if so, sending the identified frequency to a frequency mixing module for compensation, and starting a frequency locking loop. The FFT spectrum analysis module mainly considers the following aspects: (1) since the signal frequency search range is constrained by the input signal doppler and local clock frequency drift, the FFT observed signal frequency range needs to cover the frequency search range. (2) When the spectral line is judged, a proper threshold needs to be set, and the windowing processing is carried out on the spectral line of the frequency domain, so that the central frequency value of the useful signal carrier wave is identified. (3) In order to improve the frequency discrimination accuracy, the frequency resolution of the FFT needs to have certain requirements. (4) The implementation complexity of FFT is directly related to the number of FFT operation points, for programmable integrated circuits such as FPGA, DSP and the like, the operation complexity directly influences the data storage depth and the processing time, and the number of FFT points is 512.

In the tracking stage, the FFT spectrum analysis module keeps working, the symmetry of the spectrum is monitored, and if the spectrum is abnormal, an error signal is given to the frequency locking ring to reset.

Those skilled in the art will appreciate that the details of the invention not described in detail in the specification are within the skill of those skilled in the art.

Claims

1. A capture algorithm based on a USB measurement and control system is characterized by comprising the following steps:

step 1): initial phase of capture

step 2): stage for judging whether signal is effective

step 3): in the tracking phase

The FFT spectrum analysis module keeps working, monitors the symmetry of the frequency spectrum, and if the frequency spectrum is found to be abnormal, an error signal is given to reset the frequency locking ring.

2. The capture algorithm based on the USB measurement and control system according to claim 1, wherein the filtered signal forming process is: the input digital intermediate frequency signal and SIN/COS signal generated by NCO are mixed separately to form orthogonal I path signal and Q path signal, and low pass filtering is performed to filter out high frequency component.

3. The capture algorithm based on the USB measurement and control system according to claim 1, wherein the number of FFT calculation points in step 1) is 512 points.

4. The capturing algorithm based on the USB measurement and control system according to claim 1, wherein the input signal is determined to be valid in step 2), the center value after the sequential ordering of the frequency points is used as the frequency value of the residual carrier, and is compensated to the frequency mixing module, and a start signal is generated at the same time for starting the FLL loop to operate, and the FLL loop accurately tracks the residual carrier frequency.